Abandoned mine lands pose serious threats to human health, safety, and the environment. There are as many as 500,000 abandoned mines in the United States. They exist on private and federal lands. Many are near recreational and fishing areas.

Most abandoned coal mines are in the East, primarily in Kentucky, Pennsylvania, and West Virginia. Most abandoned ore and metal mines are in the West. Most abandoned uranium mines are in Arizona, Colorado, New Mexico, Utah, and Wyoming.

There are approximately 31,000 abandoned mines on public lands, including hardrock mines, such as metals and ore mines, coal mines, and uranium mines. Approximately 26,721 of these abandoned mines are in the Southwest.

Abandoned mine sites include dangerous vertical mine shafts and unstable horizontal openings. Old support structures may be rotten and cause cave-ins. There may be pockets of air in the mines with little or no oxygen.

Abandoned mines can contain or release carbon dioxide and methane, which are greenhouse gases that contribute to global warming and climate change. The greenhouse effect from mines is small. However, methane can form an explosive mixture when mixed with air, especially in enclosed mines.

Soil and water in abandoned mines may be contaminated with cyanide, lead, arsenic, mercury, and other toxic chemicals.

Unused or misfired explosives left behind in abandoned mines can become unstable and deadly. Loose materials in piles or trash heaps can collapse on hikers. Mine sites may include stockpiled waste rock and waste piles, power lines, abandoned heavy equipment, fuel storage tanks, electric machinery, and radioactive materials.

Open pits may be filled with water that can be highly acidic or contaminated with chemicals. Water-filled quarries can hide hazards such as rock ledges and old machinery.

Abandoned mines may serve as habitat for rattlesnakes, bears, mountain lions, and bats.

Abandoned uranium mines may contain fuels, solvents, degreasers, and other chemicals used with heavy equipment and rock blasting operations.

Abandoned uranium mines may contain uranium tailings, which are radioactive, sand-like materials left over from uranium milling. Uranium tailings contain radium, which stays radioactive for thousands of years. Radium decays to produce radon. Tailings can also contain selenium and thorium.

From 1944 to 1986, uranium was extracted from Navajo lands in the Four Corners (Arizona, New Mexico, Colorado, and Utah) area of the Southwest. Uranium mining is no longer allowed on Navajo lands.

When uranium mining ceased, mining companies abandoned mines without sealing tunnel openings, filling pits, or removing uranium tailings. Depending on how they are counted, at least 520 and as many as 1,032 of these abandoned sites remain throughout the Navajo Nation today.

Abandoned uranium mines and pits on Navajo lands are sometimes used for swimming, recreation, and livestock containment, exposing people and livestock to radiation. Open mine pits are sometimes used for illegal trash dumping. Abandoned uranium mines continue to expose families living nearby to radioactive waste.

The Northeast Church Rock Mine in New Mexico is the Environmental Protection Agency’s highest priority for cleaning up abandoned mines on the Navajo Nation.

This description is based on the information found in the Web links listed with this topic.